class Base64 {
  private _keyStr = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
  encode (input: string) {
      let output = ''
      let chr1, chr2, chr3, enc1, enc2, enc3, enc4
      let i = 0
      input = this._utf8_encode(input)
      while (i < input.length) {
          chr1 = input.charCodeAt(i++)
          chr2 = input.charCodeAt(i++)
          chr3 = input.charCodeAt(i++)
          enc1 = chr1 >> 2
          enc2 = ((chr1 & 3) << 4) | (chr2 >> 4)
          enc3 = ((chr2 & 15) << 2) | (chr3 >> 6)
          enc4 = chr3 & 63
          if (isNaN(chr2)) {
              enc3 = enc4 = 64
          } else if (isNaN(chr3)) {
              enc4 = 64
          }
          output = output +
              this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +
              this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4)
      }
      return output
  }
  decode (input: string) {
      let output = ''
      let chr1, chr2, chr3
      let enc1, enc2, enc3, enc4
      let i = 0
      input = input.replace(/[^A-Za-z0-9]/g, '')
      while (i < input.length) {
          enc1 = this._keyStr.indexOf(input.charAt(i++))
          enc2 = this._keyStr.indexOf(input.charAt(i++))
          enc3 = this._keyStr.indexOf(input.charAt(i++))
          enc4 = this._keyStr.indexOf(input.charAt(i++))
          chr1 = (enc1 << 2) | (enc2 >> 4)
          chr2 = ((enc2 & 15) << 4) | (enc3 >> 2)
          chr3 = ((enc3 & 3) << 6) | enc4
          output = output + String.fromCharCode(chr1)
          if (enc3 != 64) {
              output = output + String.fromCharCode(chr2)
          }
          if (enc4 != 64) {
              output = output + String.fromCharCode(chr3)
          }
      }
      output = this._utf8_decode(output)
      return output
  }
  _utf8_encode (string: string) {
      string = string.replace(/\r\n/g, '\n')
      let utftext = ''
      for (let n = 0; n < string.length; n++) {
          const c = string.charCodeAt(n)
          if (c < 128) {
              utftext += String.fromCharCode(c)
          } else if ((c > 127) && (c < 2048)) {
              utftext += String.fromCharCode((c >> 6) | 192)
              utftext += String.fromCharCode((c & 63) | 128)
          } else {
              utftext += String.fromCharCode((c >> 12) | 224)
              utftext += String.fromCharCode(((c >> 6) & 63) | 128)
              utftext += String.fromCharCode((c & 63) | 128)
          }
      }
      return utftext
  }
  _utf8_decode (utftext: string) {
      let string = ''
      let i = 0
      let c = 0
      let c1 = 0
      let c2 = 0
      while (i < utftext.length) {
          c = utftext.charCodeAt(i)
          if (c < 128) {
              string += String.fromCharCode(c)
              i++
          } else if ((c > 191) && (c < 224)) {
              c1 = utftext.charCodeAt(i + 1)
              string += String.fromCharCode(((c & 31) << 6) | (c1 & 63))
              i += 2
          } else {
              c1 = utftext.charCodeAt(i + 1)
              c2 = utftext.charCodeAt(i + 2)
              string += String.fromCharCode(((c & 15) << 12) | ((c1 & 63) << 6) | (c2 & 63))
              i += 3
          }
      }
      return string
  }
}
export default Base64
